1) Field of the Invention
The present invention is directed to a device and method of use for producing buoyancy in autonomous undersea sensor platforms.
2) Description of Prior Art
The cation H+ is continuously generated in seawater in accordance with the following chemical equilibrium (units are moles/liter): [H+][OH−]=10−14.
For autonomous undersea sensor platforms, it is desirable that the platforms be able to adjust their buoyancy so that the platforms can change their depth in a water column. The ability to rise to shallow depths, or even to the surface for brief intervals to send/receive data or instructions is a necessity. In most instances, such a platform will prefer to remain neutrally-buoyant so that the platform can remain at a pre-determined depth. The issue is how to regulate the platform depth while simultaneously minimizing the weight and size of the device or materials that control the operational depth of the platform.
An easy way to affect the depth of such a platform is to generate a gas that is used to increase buoyancy. To rise in the water column, gas is generated. To sink to a lower depth, the previously-generated and stored gas is released.
The necessary amount of gas can be generated using a chemical reaction with materials that are carried or stored on the platform or using a chemical reaction that involves some chemical species present in the ambient environment (i.e., seawater).
Using a chemical reaction with materials stored on the platform is undesirable because the materials require storage of some active material within the platform. This storage uses payload space and weight that can be used for other functions (sensing, power, etc.). In addition, depletion of the stored active material changes the overall buoyancy of the platform; thereby, limiting the duration of the mission. The stored active material is a finite resource that cannot be replenished once the platform is deployed.
Using a chemical reaction that involves some chemical species present in the ambient environment is more desirable, because the raw materials necessary for the chemical reaction to function are present at the platform after deployment. A suitable chemical reaction could take advantage of the two gases (hydrogen and oxygen) that can be generated when water is broken down by electrolysis: 2H2O→2H2 (g)+O2 (g).
The problem with the use of electrolysis is the considerable amount of energy that is required to break the chemical bonds in water between hydrogen and oxygen. Using a system and process based on electrolysis requires the dedication of a significant portion of the platform power supply to water electrolysis (an undesirable outcome that would unnecessarily limit the size and power of the platform payload).